How Vision Works

Blindness

Legal blindness is usually defined as visual acuity less than 20/200 with corrective lenses. Now that you have learned some anatomy of the eye and how it functions, it becomes easier to understand how the following conditions can lead to blindness:

Cataracts - This is a cloudiness in the lens that blocks light from reaching the retina. It becomes more common as we age, but babies can be born with a cataract. As it worsens, it can require surgery to remove the lens and place an intraocular lens.

Glaucoma - If the aqueous humor does not drain out correctly, then pressure builds up in the eye. This causes the cells and nerve fibers in the back of the eye to die. This can be treated with medications and surgery.

Diabetic retinopathy - Persons with diabetes can get blockage of blood vessels, leakage of blood vessels and scarring that can lead to blindness. This can be treated with laser surgery.

Macular degeneration - In some persons, the macula (which is responsible for fine detail in the center of vision) can deteriorate with age for unknown reasons. This causes loss of central vision. This can sometimes be helped with laser surgery.

Retinitis pigmentosa - This is an inherited disease that causes a degeneration of the retina and excess pigment. It first causes night blindness and then tunnel vision, which often gradually progresses to total blindness. There is no known treatment.

Trachoma - This is an infection caused by an organism called Chlamydia trachomatis. It is a common cause of blindness worldwide but is rare in the United States. It can be treated with antibiotics.

There are many other causes of blindness, such as vitamin A deficiency, tumors, strokes, neurological diseases, other infections, hereditary diseases and toxins. For more information, check out the links on the next page.